Morphology of Fluid Flow Channels in Reactive Porous Media

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January 1, 2002DOEI Project Funded: 2002

Proposed Research

Fluid flow channels form by reactions between migrating fluid
and solid, porous media. Determining the factors that govern the
spatial organization of focused porous flow is essential to understanding
melt transport in the upper mantle, localization of volcanic eruptions,
localization of seafloor hydrothermal vents, gas hydrate formation
and dissolution along sedimented continental margins, and groundwater
flow through calcareous sediments. However, the phenomena that
control formation of channels have only recently become computationally
tractable.

We will study the spatial distribution of fluid flow channels formed by reactive
transport of fluid via laboratory experiments, mathematical analysis, and numerical
modeling. Our goal is to better understand how the spatial distribution of
channels formed by flow along a gradient in which the solubility of the solid
increases changes as small channels coalesce into larger conduits, thereby
determining the ultimate scale of flow localization.

Final Report

What were the primary questions you were trying to address with
this research? (Or, if more appropriate, was there a hypothesis
or theory that you were trying to prove or disprove?)The primary goal is to learn how flow of magma is focused
as it moves along, and whether drainage channels can branch out
into more channels again.

What have you discovered or learned that you didn't know before
you started this work?We learned a little more about how
to set these experiments up. Drainage channels have been produced,
but the branching of channels has not been found at all.

What is the significance of your findings for others working in
this field of inquiry and for the broader scientific community?Nothing yet, the project was only intended to start this
work.

What is the significance of this research for society?Ultimately to know volcano mechanics better, to understand
how magma interacts with host rock as it flows along.

What were the most unusual or unexpected results and opportunities
in this investigation?The biggest surprise to us is how
hard it is to get flows to focus into channels when we want that
to happen, and yet we know experiments where the channelization
is easy to make. The
branching of channels, which is seen in geological settings,
is not found in our laboratory experiments.

What were the greatest challenges and difficulties?Working
with saturated salt solutions. They corrode
metals easily, are tough on one’s skin, and their properties
are not well quantified.

When and where was this investigation conducted? The purpose was to design and begin to run new experiments
in the Geophysical Fluid Dynamics Laboratory.

What were the key tools or instruments you used to conduct this
research?Densiometer, thermometers, temperature baths, custom made
containers and lots of mathematics and searching out properties
of materials.

Is this research part of a larger project or program?Conceptually yes, but the projects are not funded.

What are your next steps?One of us has started using a wax-like polyethylene glycol
instead of saturated salt solutions and in this one channels
are easy to make.

Have you published findings or web pages related to this research? No,
except Braun’s thesis does have discussion of
the experiments, but the experiments enrich his understanding. There
will be no publication of these results in their own right, this
project is not able to support that level of scientific achievement.

Please provide some biographical information, such as place of
birth, degrees earned, significant awards or honors, research interests,
reasons why you became a scientist or why you are interested in
this line of research, and any personal interests, hobbies, or
details that you are willing to share. You can find a few good
examples here:Peter Kelemen is a field geologist and petrologist
interested in how rocks are formed during magma flow. He
just received the Bowen Award from the Volcanology, Geochemistry,
and Petrology Section of the American Geophysical Union. After
extensive field studies, he became interested in working with Jack
Whitehead who is a fluid dynamicist and has developed more than forty
new laboratory experiments in his career. They have jointly
worked toward developing fluid mechanics studies to study melt-rock
interaction starting about ten years ago, This project teaches
about the effects of crystallization on flow focusing using saturated
salt solutions. Mike Braun conducted extensive studies of magma
drainage mechanisms for his thesis work and the preliminary experiments
done here by Mike and other students in the geldynamics program produced
new refined experiments.

RESEARCH SUMMARY:
A number of laboratory experiments were constructed
in which water flowed through salt crystals and caused the crystals
either to grow due to the water reaching saturation temperature,
or to dissolve if the water was below saturation. We sought to
view spatial organization of drainage channels in the salt matrix.
A number of geological applications for flow focusing exist in
magma systems, including processes leading to dunites in Ophiolites
(ancient ocean floors that have been thrust up on land), flow focusing
under spreading centers that leads to dunites, channelization of
magma in surface volcanic systems, and erosion within limestone.
The salt used was Ammonium Chloride, which has a solubility coefficient
in water that is very dependent on temperature. A few experiments
were conducted with syrup rather than salt solution. In the project
a number of experiments were conducted by students, especially
by Mike Braun in conjunctions with interests he developed in his
thesis work. Funds were used principally to construct the equipment
and purchase the materials. A small amount of funds were used to
design the experiments and help with data analysis. The projects
are summarized below: The reports are in the form of Geodynamics
project reports or informal notes. At present, there are no plans
for publications, although some of the results might be in future
papers.

Lisa Lassner: Spring 2003. Used small 16cm x
16 cm x 16 cm tank for crystal growth experiment related to ledge
formation on hydrothermal vents. We used supersaturated KNO3
liquid in the tank. A heater/cooler unit with a 50/50 antifreeze
mix supplied cold fluid of about - 7 degrees C to a 1/2 cm diameter
stainless steel tube placed horizontally in the tank. Crystals
then grew on the tube presenting ledge-like features. (Photo
of ledge is in the Gizmos' section of our website.)

Christina Kaba: Spring 2003. Built a flat tray about 40
cm square. One end of the tray was constructed of 1/2" aluminum
about 15cm wide, the remainder of the tray was acrylic. Beneath
the aluminum section was a chamber connected to a heater cooler
unit that supplied cold water at about 2 degrees C , which cooled
the aluminum. A thin acrylic cover was placed above
the entire tray and spaced above it using small glass beads. Supersaturated
NH4CL was supplied to a manifold and uniformly distributed it in
a line above the aluminum plate. The super-saturated liquid
hit the cold aluminum, crystallized and eventually formed channels
through the crystallized salt. The glass beads provided channels
to the non-cooled sections of the tray and other channels developed.

Mike Braun: (I) summer 2002: Built 60cm (l)
x 20 cm (h) by 1/2" (w) of thick acrylic. At the top
and bottom were 1/2" diameter stainless steel tubes that ran
the length of the tank. Heating and cooling units supplied
water to the tubes at fixed temperatures. A saturated sodium
nitrate solution filled the tank. The lower stainless tube
was 5 deg. C and the upper tube was 40 deg. C. The top fluid
was in contact with solid crystals and became saturated and hence
dense. It sank to the bottom where rising cold liquid would
not be saturated upon rising and getting warmer and it would form
dissolution channels through the salt. These eventually form
mineature vents with rising lower salinity liquid emerging from
their tops as shown in shadow graphs. (Photo is available
on our website in photo gallery 'experiments'.)

Mike Braun: (II) Spring 2003: An expansion of his first experiment. Used
supersaturated NH4Cl rather than Sodium Nitrate. Built much
more complicate tank with a 1' thick acrylic test section to insulate
the fluid. A bottom tank about 78 cm (l) x 14cm (h) x 13cm
(w) was a holding tank for the liquid and was heated by a 1/2'
stainless steel tube. The NH4Cl was continuously pumped into this
tank. Above it was placed the test chamber about 76cm(l)
x 27 cm(h) x 1/2" (w). Four stainless steel 1/2" tubes
(two at the top and two at the bottom) were recessed into the 1" thick
sidewalls. They ran horizontally and supplied either warm
or cool water from two heater coolers. The test chamber was
filled with glass spheres to aid in channel development from the
crystallizing salts. Finally, above the test chamber was
a long tank that caught the rising fluid and recycled it to the
supply system. (Photo in Gizmo section of website.)

Mike ran short of time with experiment II. He had planned
to study the crystallization process with different flow rates
and concentrations. He wanted to observe the change in liquid
composition by sampling the supply fluid before it was cooled and
its concentration as it left the system to be recycled. He had
hoped to observe the flow channels in detail.

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